Hi-
Found a guy on the web who was a beta tester for the Touch and also took it apart to mod it. In response to a query from me, he responded:
the touch has two crystals, one which handles 44.1 and 88.2 and the
other handles 48 and 96.
There is no built in clock input, but you can fairly easily mod it to
take an external clock and feed it into the crystal inputs.
The frequencies are:
22.5792 MHz for 44.1 and 88.2
24.576 MHz for 48 and 96